Seismometer spring suspension system

ABSTRACT

A spring suspension system for a seismometer for suspending one body relative to the second body including three resilient leaf cantilever springs each including two adjacently positioned leaf arc segments extending approximately 120* with the second ends of adjacent segments connected together and the first ends of adjacent segments being connected respectively to the first and second bodies. An inner ring connected to the inner segments and an outer ring connected to the outer segments with the inner and outer rings including portions electrically insulated from each other to provide two separate electrical conducting paths. A spiral electrical conducting spring connected to each separate electrical path, one end of which is fixed and the second end limiting rotational movement of the leaf spring.

tilted States atent 1 Wilson et a1.

[ SEISMOMETER SPRING SUSPENSION SYSTEM [76] Inventors: Ernest Wilson,10031 Larston, 1 Houston, Tex. 77055; Allen H.

Mueller, 304 W. 31st St., Houston, Tex. 77018 [22] Filed: Sept. 7, 1971[21] Appl. No.: 178,030

[56] References Cited UNITED STATES PATENTS I 3,239,804 3/1966 Elskamp267/161 3,582,875 6/1971 Wambeck 340/17 3,344,397 9/1967 Elliott 267/160[111 3,73,445 June 12, 1973 [5 7] ABSTRACT A spring suspension systemfor a seismometer for suspending one body relative to the second bodyincluding three resilient leaf cantilever springs each including twoadjacently positioned leaf arc segments extending approximately 120 withthe second ends of adjacent segments connected together and the firstends of adjacent segments being connected respectively to the first andsecond bodies. An inner ring connected to the inner segments and anouter ring connected to the outer segments with the inner and outerrings including portions electrically insulated from each other toprovide two separate electrical conducting paths. A spiral electricalconducting spring connected to each separate electrical path, one end ofwhich is fixed and the second end limiting rotational movement of theleaf spring.

9 Claims, 14 Drawing Figures PATENIED 738,445

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ERNEST WILSON ALLEN H. MUELLER, INVENTORS 1 SEISMOMETER SPRINGSUSPENSION SYSTEM BACKGROUND OF THE INVENTION Seismometers of the typetypically used in geophysical land reflection exploration generallyconsists of l a spring suspended mass in a (2) supporting frame and (3)means to measure the relative motion between the mass and the frame.Such seismometers commonly employ flat leaf springs to suspend the mass.The conventional spring is generally a uniform tri-flexure spring withthe flexures having a single arc like form subtending approximately 120and being circularly arranged with the ends joined to an inner and outersupport ring.

The intrinsic linear range of a seismometer spring must be greater asits diameter becomes smaller, or as the natural frequency of thespring-mass system becomes lower. Since land type seismometers havetended toward small size and low frequency, the conventional seismometerspring has become marginal in performance under these conditions.Furthermore,

prior leaf springs tend to generate an internal torsional I force whichgenerates distortion in the output signal. Furthermore, the leaf springsof the prior art seismometers were often permanently deformed byexternally applied torsional forces.

Generally, the suspended mass is an electrical coil and the methods ofelectrically interconnecting the coil to external terminals have createdadditional problems in connection with the spring. Generally, twomethods of electrically connecting the coil have been used. First, twoseparate flexible electrical conductors, known as pigtails, have beenused in the past to directly bridge from the coil to the externalelectrical terminals. The pigtails are attached only by their ends andare otherwise self-supporting. Because of their nature, the angularposition of the coil assembly must be fixed relative to the frame thusrequiring the springssupporting the coil to be fixed to the frame. Withthe pigtail type electrical connections, any rotational accelerationsapplied external to the seismometer generate a torsional force betweenthe frame and the suspended mass of the coil which must be supported bythe spring and large rotational accelerations often permanently deformthe springs of seismometers.

In order to avoid the use of pigtails, a second method of electricalinterconnect utilizing slip rings has been in common use. In thismethod, the springs form part of the sliding contacts which allowrotation of the coil relative to the frame thereby protecting thesprings from rotational accelerations. However, slip rings have certaindisadvantages in that they require precious metal plating in order toovercome the problem of surface oxidation and to minimize contactresistance of the electrical interconnecting parts.

The present invention is directed to providing an improved springsuspension system for a seismometer for overcoming the prior artproblems.

SUMMARY The present invention is directed to a spring suspension systemfor a seismometer for obtaining the maximum spring linearity consistantwith good radial stability by providing three resilient leaf springspositioned between an inner and outer support ring with each springincluding two adjacently positioned leaf arc elements radially displacedfrom each other and extending approximately 120 with the first end ofthe segments being connected to the inner and outer ring, respectively,and the second ends of the adjacent segments being connected together.

Yet a still further object of the present invention is the provision ofan electrical spring suspension system having at least two separateelectrical conducting paths through the spring subjecting theseismometer springs to excess rotational.

Still a further object of the present invention is to adequately protectthe seismometer springs against certain externally applied rotationalaccelerations while avoiding the use of slip rings by providing a spiralelectrical conducting spring connected to the seismometer spring whichprovides an electrical path and which allows a limited rotationalmovement of the suspended mass with respect to the frame.

Still a further object of the present invention is to facilitate the useof a one piece coil form, with its corresponding high mass to volumecapability and/or ease of manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section elevationalview of an embodiment ofa dual coil seismometer utilizing the presentinvention,

FIG. 2 is a plan view ofa top leaf spring ofthe present invention, priorto assembly,

FIG. 3 is a plan view of a bottom leaf spring of the present invention,

FIG. 4 is a sectional view of a portion of the bottom leaf spring ofFIG. 3 delineated by lines 4-4 illustrating its free lengthconfiguration,

FIG. 5 is a plan view of an upper spring hub,

FIG. 6 is an end view of the upper spring hub of FIG.

FIG. 7 is a plan view of a lower spring hub,

FIG. 8 is a plan view of an upper spiral interconnect of the presentinvention,

FIG. 9 is an end view of the upper spiral interconnect of FIG. 8,

FIG. 10 is a plan view of a lower spiral interconnect of the presentinvention,

FIG. 11 is an end view of the lower spiral interconnect of FIG. 10,

FIG. 12 is a plan view of a top disc insulator,

FIG. 13 is a plan view of a separator disc insulator, and

FIG. 14 is a plan view of a retainer disc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The spring suspension system ofthe present invention will be described, for purposes of illustrationonly, as used in a dual coil type seismometer of the class typicallyused in land geophysical exploration, but it is understood that thepresent invention is suitable for use in other types of seismometers.

Referring now to FIG. 1, a dual coil seismometer, generally referred toas 10, includes air gaps 21 and 22 which are energized by a centrallypositioned, cylindrical permanent magnet 23. This magnet is supportedwithin the frame by two magnetic pole caps 24 and 25. Additionally, thepole caps serve to conduct magnetic lines of flux between a magnet poleface 26 and air gap 21, as well as between pole face 27 and air gap 22.The magnetic circuit is completed external to the air gaps by acylindrical, magnetic, seismometer case, 28.

The top 31 and bottom caps 32 are made from a nonmagnetic material andare retained and sealed by swaged case ends onto O-rings 33 and 34.Holes 35 and 36 in the top 31 and bottom cap 32, respectively, retainconcentrically the magnet and pole cap assembly 23, 24, and 25. O-ring37 compensates for make up tolerances between the top and bottom cap andthe case, and the top and bottom cap and the magnet assembly. Insulatedterminals 38 and 39 located in the top cap 31, provide for externalelectrical connection.

A cylindrical, non-magnetic coil form 40, wound with two coils, 41 and42, is suspended within the two air gaps 21 and 22, and other spaceprovided, by a top spring 43 and a bottom spring 44. The two coils areconnected in series along an axial slot 45 in the coil form. Theremaining two coil wires are similarly brought up and connected to thetop spring at 46 and 47.

Thus, in the present embodiment the case 28 and magnet 23 serves as afixed reference support while the coils 41 and 42 serve as the inertiamass with the top spring 43 and the bottom spring 44 suspending thecoils 41 and 42 relative to the magnet 23 so that relative vibratingacceleration forces cause movement of the coils 41 and 42 relative tothe magnet 23 which induces a voltage signal in the coils.

Referring now to FIG. 3, which depicts the basic springs configurationof the present invention, which may be described as a uniformtri-flexure leaf spring 44. Spring 44 includes three resilient leafsprings each of which includes two adjacent are like segments. The firstspring includes two segments, the first of which is defined by flexureends 48 and 49 and the second of which includes flexure ends 50 and 51.The second leaf spring includes two segments, one segment defined byflexure ends 52 and 53 and the second segment defined by flexure ends 54and 55. The third leaf spring includes two segments, the first of whichis defined by flexure ends 56 and 57 and the second of which is definedby flexure ends 58 and 59. All of the arc segments are circularlyarranged in the same direction and are all intermediately positionedwith respect to an inner support ring 60 and an outer support ring 61.Each pair of arc segments are radially displaced with each other, forexample, segment 48-49 being radially displaced from segment 50-51. Andeach segment as well as both segments comprising a spring togethersubtend approximately 120 of arc of the spring. Accordingly, within aspring, the outer most segment will have two ends adjacent the two endsof the inner most segment, for example, referring to segment 48-49 andsegment 50-51, end 49 is adjacent to end 50 and end 48 is adjacent toend 51. Also, end 49 and end 50 are joined one to the other, and the end48 and end 51 are joined to the outer support ring 61 and the innersupport ring 60, respectively. Thus, all of the arc segments arecantilevered and flex about the flexure ends 48-59.

The leaf spring 44 of FIG. 3 as well as the leaf spring 43 of FIG. 2 ismanufactured by the photo etch process from a thin sheet of non-magneticspring material, such as beryllium copper alloy, with a thicknessusually between 0.004 inch and 0.007 inch. The etched spring is thenappropriately heat treated in a properly designed fixture to yield aspring whose freelength condition is as depicted in FIG. 4. Suchproperly sized seismometer springs return to their flat condition whenin equilibrium with their load. Referring to FIG. 1, spring 43 andspring 44 are two such springs supporting the seismometer coil assembly.

As previously stated, conventional seismometer springs embody threesingle segments. Referring to FIG. 3, a conventional seismometer springcan be illustrated by omitting the three innermost flexure segments50-51, 54-55, and 58-59, and reconnecting the remaining flexure segmentsto the inner support ring by bridging 50 to 55, 54 to 59, and 58 to 51.(FIG. 4 would now reflect the omission of flexure segment 50-51 and thebridging of 50 to 55.)

Now if the outer support ring 61 of a conventional spring were fixed ina plane, and the inner support ring caused to be displaced axially withrespect to that plane, it should be evident that a slightcounterclockwise movement of the inner support ring 60 must accompanyeither an upward or a downward displacement of the inner support ringfrom that plane. This is, of course, due to the fact that the projectedimage of the flexure to the plane of the outer support ring 61 becomesshorter as the inner support ring 60 is displaced farther from the flatposition. It should also be appreciated that although the same must besaid regarding the projected image of flexure segments of the presentinvention, two such actions are caused to oppose one another. Thereforethe spring 44 of FIG. 3, and of the present invention, can be describedas being rotation cancelling.

A comparison of performance of the springs of the present invention asdepicted in FIG. 3 to that of the conventional spring of the prior artwill now be made. Since both the present and the conventional spring arethree flexure springs, the comparison will be made on the basis of onesegment, with the inside diameter of the outer support ring 61 being thesame in both cases. Also rectangular flexure segments will be assumed.

Of a single leaf cantilever spring with such a section it can bewritten:

where d Displacement L Length of cantilever S Tensile or compressivestress E Modulus of Elasticity t Thickness of cantilever Now the lengthof the flexure segments 48-49 and 50-51 of the present spring are equaland in a typical application measure 0.580 inch each. Also the segments48-49 and 50-51 are comprised of four cantilever sections 48-62, 62-49,50-63, 63-51 joined end to end with fixed cantilever ends being located48, 49, 50, and 51, and free cantilever ends being joined at 62 and 63.Therefore, each spring consists of four cantilever sections, end to end,each cantilever being 0.580/2, and

2 2 (0.580/2 s l/s E 1,

where d displacement of present spring.

Similarly, a segment of a prior art spring can be shown to consist oftwo cantilever sections joined end to end. Since equal segment length isnot a consideration, the flexure segment length of the conventionalspring is somewhat longer, making use of the space comparable to 64 ofFIG. 3. Therefore, the flexure segment length of a conventionalequivalent is 0.670 inch, each cantilever section being 0670/2, and

where d, displacement of conventional spring Now comparing d to d Let s,s,, E, 15,, r, =1,

Therefore it can be stated that the present spring of FIG. 3 basicallyhas a linear range of approximately 150 percent that of the conventionalseismometer spring. Additionally, it should be clear that a somewhatgreater improvement in displacement may be obtained by increasing thelength of the outermost flexure segments so as to make use of spaces 64,65, and 66, thereby accepting only partial rotational cancelling. Ineither case, the basic linearity will be greater than, and therotational effects less than those of the conventional seismometerspring.

It should however also be appreciated, that while the basic linearity ofthe improved spring of the present invention is increased, lateralstability and strength are to a great extent maintained. Three flexuresjoined to the inner and outer support rings at 120 intervals causes thespring to exhibit near uniform radial stiffness characteristics.

Referring to FIG. 1, the bottom leaf spring 44, is that spring depictedin FIG. 3. An inner support ring 60, of the bottom spring 44 is a slipfit over a bottom central boss 67 of the bottom cap. Also the outersupport ring 61, of the bottom spring 44 is a slip fit into a springrecess 68 of the coil form 40, being maintained in its position by thenormal tension of the bottom spring 44. In such a suspension system,where the bottom spring 44 is disassociated from electricalinterconnects, it is practical to adjust the natural frequency to closetolerances by individually selecting a bottom spring of the requiredthickness. Access to the bottom spring is obtained before swaging caseend 29 by inverting the seismometer and lifting case 28, bottom cap 32,O-ring 34, bottom spring 44, and O-ring 37 from the remaining componentsof the seismometer. Removal of O-ring 37 then allows replacement ofspring 44. Reassembly is performed by the reverse procedure.

The basic spring configuration of the top spring 43 of FIG. 1 isidentical to that of the previously described FIG. 3. Additionally, thetop spring functions as the two electrical interconnects to the coil,and is therefore arranged to form two separate electrically conductingpaths between its corresponding inner and outer sup port rings.Accordingly, the inner support ring and the outer support ring of thetop spring are separated after being assembled into their predeterminedfixed positions. The top spring, prior to assembly, is depicted in FIG.2.

Referring to FIG. 1, an inner support ring 68 (also in FIG. 2) is heldin position between an upper spring hub 69 (also FIG. 5 and FIG. 6) anda lower spring hub 70 (also FIG. 7) by four eyelets. Eyelets 71 and 72are two of the eyelets which are in view. Eyelet 71 passes through hole73 of hub 69 (FIG. 5), hole 74 of spring 43 (FIG. 2), and hole 75 of hub70 (FIG. 7), eyelet 72 passes through holes 76 of hub 69, 77 of spring43, and 78 of hub 70. In like manner, the remaining two eyelets passthrough holes 79, 80, and 81, and through holes 82, 83, and 84. Theinner support ring 68, being fixed in this manner by four flairedeyelets, is separated by removing bridges and 86 of FIG. 2 One method ofseparating the inner support ring is by drilling into each bridgethrough drill guide holes 87 and 88 of the upper spring hub 69.

The upper and lower spring hubs 69 and 70 are composed of anelectrically insulating material. These spring hubs are economicallymanufactured to close tolerances by an injection molding process.Various commercially available thermoset molding compounds are suitablefor this application.

Referring again to FIG. 1, the outer support ring 89 (also in FIG. 2)40. Appropriate fillers in the adhesive space the spring and the coilform a small amount, causing the joint to be electrically insulating.The coil form is prepared for the adhesive by etching to a dull finish.

Referring again to FIG. 2, the radial slots in the outer support ring,such as slot 90, provide additional interlocking means for the adhesive.Alignment tabs 91, 92, and 93 are bent downward approximately 30 fromthe plane of the spring, at perforations 94, 95, and 96, respectively.These tabs accurately center the top spring 43 to the coil form 40.Subsequent to the bonding process, the three alignment tabs 91, 92 and93 are removed, and the outer support ring 89 of the top spring isseparated by breaking off along the lines formed by perforations 97-98,99-100, and 101-102. In this manner the coil wire soldered at 46 iselectrically connected through a flexure spring 103 by the eyelet inhole 83, and the coil wire soldered at 47 is electrically connectedthrough the remaining two flexure springs to the eyelet in hole 80. Thesmall tabs 104 and 105 associated with eyelet holes 80 and 83, springagainst their respective eyelets with a sharp edge, insuring positiveelectrical connection.

The spiral interconnections 120 and 115 of FIG. 8 and FIG. 10, inconjunction with the separated top spring, provided an improved methodof electrically interconnecting the seismometer terminals to the coils41 and 42, while protecting seismometer spring 43 from excess externallyapplied rotational accelerations. The outside ends 107 and 109 of thespiral interconnects 120 and 115 are fixed to terminals 38 and 39 in thecase top; the inside ends 108 and 110 of the spiral interconnects 120and are fixed to eyelets of the spring hubs. With the spring hubs beingof a slip fit over the top central boss, 106 of FIG. 1, the coil form 40is allowed to rotate slightly more than 90 in either direction from itscentral position before completely winding up one or the other of thespiral interconnects or 115. Under zero torque conditions, the spiralinterconnects 120 or 115, acting as spiral springs, return the coil form40 approximately to its central angular rest position. Sufficientrotational damping is obtained from the normal friction between theparts involved. Additionally, the spiral interconnects 120 and 115 aredimentioned so as to produce somewhat less than the yield stress withinthe top spring at the angle of maximum rotation. Such a system ofcontrolled rotation takes advantage of the fact that the damagingrotational accelerations typically encountered in use are of a transientnature, and operate over relatively small angles. Thus, the spiralinterconnects 120 and 115 operate to substantially reduce the transientpeak rotational acceleration transmitted to the coil form 40, therebyreducing peak stresses within the seismometer springs 43 and 44.

Spiral interconnects 120 and 115, FIGS. 8, 9, 10, and 11, areeconomically manufactured from beryllium copper sheet with a thicknessof 0.015 to 0.018 by the photoetch process. Three quarter hard materialfor this application is sufficiently strong, and allows for the bendingof tabs 107 and 108 of FIG. 9, and 109 and 110 of FIG. 11. No heattreatment is required.

Referring to FIG. 1, the spiral interconnects 120 and 115 are assembledto the upper spring hub 69 (also FIGS. and 6) as follows: Retainer disc111 (also FIG. 14) is a slip fit over eccentric 112 (also FIGS. 5 and 6)and rests against step 113 of FIGS. 5 and 6. The retainer disc is a0.006 thick beryllium copper disc. The retainer disc contains the spiralinterconnects between it and top cap 31. Notch 114 of FIG. 14 alignswith hole 82 of FIG. 5. Lower spiral interconnect 115 is a slip fit overeccentric 112 with tab 110 of FIG. 11 protruding into the hollow eyeletof hole 82 of FIG. 5, where it is attached by soldering. The separatordisc insulator 116 (also FIG. 13) a punched disc of 0.0075 polyester, isa slip fit over diameter 117 (also of FIGS. 5 and 6) resting on step 118of hub 69, with notch 119 of insulator 116 aligned with hole 79 of hub69. Upper spiral interconnect 120 is a slip fit over diameter 117 of hub69 with tab 108 of interconnect 120 protruding into the hollow eyelet ofhole 79 of hub 69 where it is attached by soldering. Top disc insulator121, (also FIG. 12), a punched disc of 0.0075 polyester, is a slip fitover top central boss 106, with notches 122 and 123 ofinsulator 121 inalignment with terminals 38 and 39. Accordingly, tabs 107 and 109 passthrough terminals 38 and 39, where they are soldered.

Therefore, as previously described, the coil wires terminated at 46 and47 are electrically connected to terminals 39 and 38 through twoseparate insulated parts of the top spring 43, two eyelets, and twoseparate, insulated, spiral interconnects 120 and 115. Paths ofconnection are: (1) wire termination 46 through the eyelet in holes 83of spring 43 and 82 of hub 69, through the lower spiral interconnect115, to tab 109 in terminal 39; (2) wire termination 47 through theeyelet in holes 80 of spring 43 and 79 of hub 69, through the upperspiral interconnect 120, to tab 107 in terminal 38.

The present invention is therefore well adapted to carry out the objectsand attain the ends and advantages mentioned as well as others inherenttherein. While a presently preferred embodiment of the invention isgiven for the purpose of disclosure, numerous changes in the details ofconstruction and arrangement of parts may be made which will readilysuggest themselves to those skilled in the art and which are encompassedwithin the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A spring suspension system for a seismometer for suspending one bodyrelative to a second body comprising,

an inner support ring connected to one of the bodies,

an outer support ring positioned coaxially with the inner ring andconnected to the second body,

three resilient leaf springs being positioned between the rings,

each spring including first and second adjacently positioned arc leafsegments radially displaced from each other and extending approximatelythe first segment being adjacent the inner ring and the second segmentbeing adjacent the outer ring, each segment having first and secondends, the first ends of the first and second segments being adjacent toeach other, the second ends of the first and second segments beingadjacent to each other, said second ends of the first and secondsegments being connected together, the first end of the first segmentbeing connected to the inner ring and the first end of the secondsegment being connected to the, outer ring.

2. The apparatus of claim 1 wherein the inner and outer rings includeportions electrically insulated from each other for providing at leasttwo separate electri cally conducting paths through the inner and outerrings.

3. The apparatus of claim 1 including,

a plurality of removable alignment tabs connected to the outer ring foraligning the outer ring with the second body for bonding therewith andafterwards for removal.

4. The apparatus of claim 2 including,

a spiral electrically conducting spring connected to each separateelectrical path, one end of which is fixed and the second end limitingrotational movement of said leaf springs.

5. In a spring suspension system for a seismometer for suspending onebody relative to a second body by a spring including portionselectrically insulated from each other for providing at least twoseparate electrically conducting paths through the spring, theimprovement comprising,

a spiral electrically conducting spring connected to each separateelectrical path in said spring, one end of the spiral spring being fixedand the second end connected to and limiting rotational movement of thesuspension spring.

6. A spring suspension system for a seismometer for suspending a coilrelative to a frame comprising,

an inner support ring connected to the frame,

an outer support ring positioned coaxially with the inner ring andconnected to and supporting the coil,

three resilient cantilevered leaf springs being positioned between therings, all of which circularly extend in the same rotational direction,

each spring including first and second adjacent arc segments radiallydisplaced from each other and each extending approximately 120, thefirst segment being adjacent the inner ring and the second segment beingadjacent the outer ring, each segment having first and second ends, thesecond ends of the first and second segments being connected together,the first end of the first segment being connected to the inner ring,and the first end of the second segment being connected to the outerring.

7. The apparatus of claim 6 wherein the inner and outer rings eachinclude portions electrically insulated from each other for providing atleast two separate an inner support ring connected to one of the bodies,

an outer support ring positioned coaxially with the inner ring andconnected to the second body,

three resilient leaf springs being positioned between the rings,

said inner and outer rings including portions electrically insulatedfrom each other for providing at least two separate electricallyconducting paths through the inner and outer rings.

1. A spring suspension system for a seismometer for suspending one bodyrelative to a second body comprising, an inner support ring connected toone of the bodies, an outer support ring positioned coaxially with theinner ring and connected to the second body, three resilient leafsprings being positioned between the rings, each spring including firstand second adjacently positioned arc leaf segments radially displacedfrom each other and extending approximately 120*, the first segmentbeing adjacent the inner ring and the second segment being adjacent theouter ring, each segment having first and second ends, the first ends ofthe first and second segments being adjacent to each other, the secondends of the first and second segments being adjacent to each other, saidsecond ends of the first and second segments being connected together,the first end of the first segment being connected to the inner ring andthe first end of the second segment being connected to the outer ring.2. The apparatus of claim 1 wherein the inner and outer rings includeportions electrically insulated from each other for providing at leasttwo separate electrically conducting paths through the inner and outerrings.
 3. The apparatus of claim 1 including, a plurality of removablealignment tabs connected to the outer ring for aligning the outer ringwith the second body for bonding therewith and afterwards for removal.4. The apparatus of claim 2 including, a spiral electrically conductingspring connected to each separate electrical path, one end of which isfixed and the second end limiting rotational movement of said leafsprings.
 5. In a spring suspension system for a seismometer forsuspending one body relative to a second body by a spring includingportions electrically insulated from each other for providing at leasttwo separate electrically conducting paths through the spring, theimprovement comprising, a spiral electrically conducting springconnected to each separate electrical path in said spring, one end ofthe spiral spring being fixed and the second end connected to andlimiting rotational movement of the suspension spring.
 6. A springsuspension system for a seismometer for suspending a coil relative to aframe comprising, an inner support ring connected to the frame, an outersupport ring positioned coaxially with the inner ring and connected toand supporting the coil, three resilient cantilevered leaf springs beingpositioned between the rings, all of which circularly extend in the samerotational direction, each spring including first and second adjacentarc segments radially displaced from each other and each extendingapproximately 120*, the first segment being adjacent the inner ring andthe second segment being adjacent the outer ring, each segment havingfirst and second ends, the second ends of the first and second segmentsbeing connected together, the first end of the first segment beingconnected to the inner ring, and the first end of the second segmentbeing connected to the outer ring.
 7. The apparatus of claim 6 whereinthe inner and outer rings each include portions electrically insulatedfrom each other for providing at least two separate electricallyconducting Paths through the inner and outer rings.
 8. The apparatus ofclaim 7 including, a spiral electrically conducting spring connected toeach separate electrical path, one end of said spring being fixed andthe second end limiting rotational movement of said leaf springs.
 9. Aspring suspension system for a seismometer for suspending one bodyrelative to a second body comprising, an inner support ring connected toone of the bodies, an outer support ring positioned coaxially with theinner ring and connected to the second body, three resilient leafsprings being positioned between the rings, said inner and outer ringsincluding portions electrically insulated from each other for providingat least two separate electrically conducting paths through the innerand outer rings.